Many pieces of construction equipment use hydraulic systems to control the functions performed by the equipment. The construction equipment operator is provided with one or more input devices operably coupled to one or more hydraulic actuators, such as hydraulic cylinders, which control the relative positions of various components or devices of the equipment to perform various operations. For example, backhoes often have a plurality of control levers and/or foot pedals to control various functions of a backhoe, such as a position of a boom arm, a position of a dipperstick arm coupled to the boom arm, and a position of a bucket coupled to a dipperstick arm.
The magnitude of movement of an input device, such as a control lever, generally controls the output, i.e. force and/or velocity, of a given device, such as a dipperstick arm on a backhoe. Some operations require precision output of a given device, such as digging around an pipe with a backhoe. Under such circumstances, it is desirable to control the output of the dipperstick arm relative to the pipe or other object. Such operations would be aided by greater control of the output, such as greater control of the force and/or velocity of the dipperstick arm.
Hydraulic systems may use accumulators to store energy in the form of pressurized fluid. Accumulators may acquire pressurized fluid under the influence of an over-running load. When construction equipment lowers a load, the force of gravity on the equipment and the load provides pressurized fluid to the accumulator. This pressurized fluid can perform additional work or remain stored in an accumulator. When lowering the load, pressurized fluid is directed into the accumulator that typically has a pre-charge and fixed volume. Pressurized fluid is then available at a nearly constant pressure level from the accumulator for later reuse or distribution to various components or devices of the equipment to perform various operations.